SAN DIEGO Donald Trump brought his message of walls and deportations to the doorstep of America’s busiest border crossing on Friday as the presumptive Republican presidential nominee greeted supporters in San Diego, amid one of the largest counter-protests organized against him.

The scene inside the San Diego Convention Center during Trump's speech was relatively placid, while outside demonstrators opposed to his controversy-ridden White House bid marched and chanted, carrying signs criticizing his rhetoric against illegal immigration.

Waving U.S. and Mexican flags, more than 1,000 people turned out for anti-trump rally in San Diego, a city on the U.S.-Mexico border whose San Ysidro port of entry sees nearly 300,000 people a day cross legally between the countries.

San Diego is considered a binational city by many who live and work on opposite sides of the border, and about a third of the city's population is Latino.

Some protesters on Friday afternoon attempted to breach a barrier manned by police, climbing over railings and throwing objects at officers, who used their night sticks in an attempt to hold back the crowd.

As clusters of Trump supporters and anti-Trump demonstrators began to mix following the candidate's appearance, police declared the gathering to be an unlawful assembly and ordered people to disperse. Police reported making at least three arrests.

Trump has weathered months of blowback from all ends of the political spectrum for his immigration policy, which calls for the building of a wall along the U.S.-Mexico border and deporting the nearly 11 million undocumented immigrants who reside in the United States.

Critics have said his plan is needlessly cruel and impossible to implement. At Trump's campaign stops, attendees often chant "build the wall."

Friday was not the first time Trump has been greeted by civil unrest in California, which is home to the largest Latino population in the country. Late last month, a visit to the California Republican convention set off days of protests in the area, leading to several arrests.

WAITING FOR "FIRST PLACE FINISHER"

Shortly before taking the stage in San Diego, Trump issued a statement ruling out a one-on-one debate with second-place Democratic hopeful Bernie Sanders, who was also campaigning in California, killing off a potentially high-ratings television spectacle.

The suggested debate would have sidelined likely Democratic nominee Hillary Clinton but given Sanders a huge platform ahead of California's June 7 primary.

A day after saying he would welcome a debate with Sanders, Trump called the idea "inappropriate" because as the Republican presumptive nominee he should only face the Democrats' final choice.

"I will wait to debate the first place finisher in the Democratic Party, probably Crooked Hillary Clinton," Trump said in a statement.

Sanders’ campaign had been aggressively advocating for a debate with Trump after the idea was raised during an appearance by the New York billionaire on a talk show this week.

Sanders, a U.S. senator from Vermont, expressed disappointment on Friday.

"I heard that he was going to debate me, then I heard that he was not going to debate me, then I heard that he was going to debate me. Now you’re telling me that he is not going to debate me. Well, you know, I hope that he changes his mind again," Sanders said in a video clip posted on an ABC News Twitter account.

"Well, Mr. Trump, what are you afraid of?" he said.

Trump suggested broadcast networks were unwilling to go along with his demand that at least $10 million raised from the encounter be donated to charity.

“I’d love to debate Bernie,” he told a rally in Fresno, California. “But the networks want to keep the money for themselves.”

Sanders is trailing Clinton in the race to secure their party’s nomination, but opinion polls show he is slicing into her lead in California.

Clinton has shown no interest in debating Sanders before the California primary, which will be part of a final slate of nominating contests. It is possible she will clinch the nomination by winning New Jersey earlier that day, making the outcome in California superfluous.

The former U.S. secretary of state has said she is looking forward to debating Trump later this year ahead of the Nov. 8 general election.

Clinton leads Trump by 4 percentage points in the most recent Reuters/Ipsos poll, with their positions with voters basically unchanged since Trump’s support surged two weeks ago. Democrats nationally remain evenly split between Clinton and Sanders.

(Additional reporting by Alana Wise in Washington and Chris Kahn in New York, Steve Gorman in Los Angeles; Writing by James Oliphant; Editing by Alistair Bell and Leslie Adler)

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